The image sensor is an electronic sensor with matrix structure, consisting of an array of rows and columns with a photosensitive dot at the crossover of each row and each column. Electronic circuits are provided on the sides of the matrix to ensure the operation thereof and in particular lateral registers for controlling the row conductors and a register at the bottom of the columns for ensuring the reading of the signals detected by the individual circuits. In the case of a radiological sensor, the array is covered with a scintillator to convert X-rays into light and the luminous image resulting therefrom is detected by the array of photosensitive dots.
The matrix structure of the image sensor is in general made on a semiconductor chip of square or rectangular shape as is done for almost all integrated circuits. However, to improve the ergonomics, a proposal has already been made to make the sensor on a chip with beveled corners. After encapsulation of the chip in a protective package which hugs the shape of the chip and rounds off the corners, the sensor has a shape which is more comfortable for the patient than if the chip were rectangular.
FIG. 1 represents a chip two corners of which are beveled; these are the corners situated “at the top” in the figure, in principle at the front of the sensor in the direction of introduction of the sensor into the mouth of the patient. The signals detected by the matrix are dumped vertically from the matrix to a horizontal reading register situated at the bottom of the matrix, hence here on the rear side in the direction of introduction of the sensor, just where there are no beveled corners. The charges are then dumped horizontally by the horizontal register to an output of this register. This solution is effective in respective of comfort while introducing the sensor into the mouth; it is less so in respect of comfort while removing the sensor from the mouth.
This is why one also seeks to make a sensor having a chip with four beveled corners, that is more ergonomic both in respect of introduction into the mouth and in respect of removal. However, the room required to place a reading register at the bottom of the matrix is then no longer available.
A solution to this problem has been proposed in patent U.S. Pat. No. 5,510,623. It consists in placing a reading register vertically in the middle of the matrix, as is represented in FIG. 2, rather than horizontally at the bottom of the matrix.
In that case, the charges are dumped horizontally from the two half-matrices, left and right, to the central vertical register, then they are discharged by the vertical register to a central output situated at the bottom of the sensor. The ergonomics of the sensor is optimized by virtue of the four beveled corners, but the image is perturbed in the central zone of the sensor on account of the presence of the vertical register, even if the vertical register is itself photosensitive.